Nowadays, various functional films having various functions, e.g., optical films for liquid crystal displays such as antireflection films, anti-glare films, and optical compensation films, special films containing a heat sensitive developing agent, nano particles, and the like, separator films for fuel cells, magnetic tapes containing a magnetic agent, adhesive tapes containing an adhesive, and barrier films containing a barrier material are used.
Such a functional film is produced by applying a monolayer of a coating liquid of a multicomponent system containing a solute material having functionality onto a flat substrate or a continuously conveyed sheet substrate made of a plastic, or a metal, or the like, drying only a solvent from the coated layer, and heating and solidifying the coated layer. In formation of such a functional film, if the solute material having function can be unevenly distributed in the film surface, there are merits of improvement in functionality and significant reduction in the amount of the functional material used.
On the other hand, in the case where the solute material having functionality is unevenly distributed in the film surface, it is also considered to perform coating several times to form a multilayer coating. However, there are problems that production cost increases compared with monolayer coating, but also that a desired function cannot be demonstrated because the final coating thickness is large.
Thus, if the functional solute material can be unevenly distributed with high precision in the film surface by drying the coated layer formed by the monolayer coating, quality and cost of the functional film can be significantly improved.
However, a state inside the coated layer often changes with drying conditions, and an extremely precise control technique is demanded in order to control the state inside the coated layer precisely at the drying step to unevenly distribute the functional solute material in the film surface.
For example, Patent Document 1 is an example in which a state inside a coated layer is controlled at a drying step, although it is not for unevenly distributing a functional solute material in the film surface. In description of Patent Document 1, simulation of a two-component system is conducted to find an optimal drying condition, and the drying condition is brought closer to the optimal drying condition to prevent formation of unique depressions and projections produced in a portion at an edge of a resist film.
Moreover, change of a diffusion coefficient according to change of a solvent concentration during drying is found in Non-Patent Document 1 or Non-Patent Document 2. Particularly, a free volume theory of Duda is also tried in part in the drying simulation.
Patent Document 1: Japanese Patent Application Laid-Open No. 2003-164797
Non-Patent Document 1: AIChE Journal March 1992, Vol. 38, No. 3, pp 405-415 Predicting Polymer/Solvent Diffusion Coefficients Using Free-Volume Theory, Zielinski. J. M. Estimation of a diffusion coefficient using the free volume theory.
Non-Patent Document 2: AIChE Journal February 2003, Vol. 49, No. 2, PP 309-322 Multicomponent Diffusion Theory and Its Applications to Polymer-Solvent System, Price P. E. et al.